This is one of my findings during testing, when I disconnect the audio source the speaker don't produce any noise. But when I connect the line to the source without playing any music the speaker produces noise and when I play music the noise is not present. What do you think? Does the source (audio codec) creates noise?This is a good design. If all else fails, you might have to consider that the chip has gone bad. I have actually seen a perfectly good amplifier get noisy because of the chip. They don't always quit completely.
Actually when I play music directly from the codec without amplifier the noise is not noticeable at the speaker (using large speaker), the audio sounds good. After I place an amplifier after codec there is a noise I need higher sound level thats why I put an amplifier. I think Audioguru is right.It sounds to me as if your audio source has an automatic gain control; when no music is playing, the gain is increased until you hear noise. When music starts playing, the gain is decreased so you no longer hear the noise.
You need to figure out a way to disable that AGC circuit in the source. There is not a good way to eliminate the noise once it gets to your amplifier.
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